Question about Variable Gap and Gapmin of type 7
Hi,
I want to know if what I thought is correct.
The interface setting of two shells is as follows.
<?xml version="1.0" encoding="UTF8"?>
Top shell is 1T and bottom shell is 3T.
Distance between two shells is 2mm. > No initial penetration
Igap determines how the size of the gap is calculated.
Igap = 1
<?xml version="1.0" encoding="UTF8"?>
Then, in my model, Variable Gap = 2
And then my question is as follows.
In this model, if Gapmin is 1.5 , contact force is applied when distance between two shells is 1.5 below figure??
(when 1.5 ＜ distance between two shells, contact force is not applied??? )
Thanks
Answers

Altair Forum User said:
In this model, if Gapmin is 1.5 , contact force is applied when distance between two shells is 1.5 below figure??
(when 1.5 ＜ distance between two shells, contact force is not applied??? )
Due to Igap = 1 the variable gap will take highest value; in this case Variable Gap = max [Gapmin=1.5,(gs+gm)=2] = 2
In case the initial distance between shells is 1.5 there will be initial contact penetrations, which can be handled by Inacti=5 or 6 or Fpenmax.
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Hi,
in my model, initial distance is 2.
If External force is applied on model and gap distance is small.
And then if gap distance ≤ 1.5, contact force is applied??
Thanks
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The contact force is applied when the distance between the shells is less than the Variable gap calculated as follows for your model,
thickness slave shell = ts=1
thickness master shell = tm=3
gs=ts/2 = 0.5 mm
gm=tm/2 = 1.5 mm
Gapmin= 1.5 mm
Variable Gap = max [Gapmin,(gs+gm)]
Variable Gap = max [1.5,(0.5+1.5)] =2 mm
So the contact force will be applied when the shells are 2 mm apart.
If using variable gap then Gapmin can usually be left blank and a default value is calculated by Radioss which is typically smaller than the variable gap. However, since there are few situations where the calculated default Gapmin can be larger then the variable gap, we typically recommend setting Gapmin to a value which is 1/2 the thickness of the thinnest part.
Thanks,
Andy
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Thank you so much.
If I use variable gap, gapmin must be smaller than variable gap.
And in that case contact force is independent of gapmin value.
Is it right?
Thanks
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Andy_20955 said:
The contact force is applied when the distance between the shells is less than the Variable gap calculated as follows for your model,
thickness slave shell = ts=1
thickness master shell = tm=3
gs=ts/2 = 0.5 mm
gm=tm/2 = 1.5 mm
Gapmin= 1.5 mm
Variable Gap = max [Gapmin,(gs+gm)]
Variable Gap = max [1.5,(0.5+1.5)] =2 mm
So the contact force will be applied when the shells are 2 mm apart.
If using variable gap then Gapmin can usually be left blank and a default value is calculated by Radioss which is typically smaller than the variable gap. However, since there are few situations where the calculated default Gapmin can be larger then the variable gap, we typically recommend setting Gapmin to a value which is 1/2 the thickness of the thinnest part.
Thanks,
Andy
Thats great explination.
So if i understood well, Igap is variable gap.
Force will only act when distance between the nutral axis of both elements is less than or equal to the Variable Gap.
Where ,Variable Gap = max [1.5,(0.5+1.5)] =2 mm
Now question that bothers me is what is the penetration and instersection. Whats the difference ?
 First of all penetration concept is only valid of shell elements but solid right ?
 Second intersection concept is valid for both shell and solid ?
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